I just had a remote start installed, and I figured I'd post with some of the questions I had.
- It can be done, but the ST wiring is different from standard Focus models, so there is no "proper way" to do it.
- You lose a factory key. It's hardwired into the system to start the car, and only powered when the remote start is active.
- There are quirks. The car turns off when you open a door or unlock the door, and you have to start it again.
- It was expensive. More than double what a standard install should cost.